Mineralizer‐Assisted Synthesis of Zircon Silicate‐Based Glass‐Ceramics for High CeO ₂ Immobilization

ABSTRACT

Zircon (ZrSiO ₄ ) offers significant advantages for high‐level radioactive waste solidification due to its excellent radiation resistance and chemical inertness. However, the harsh synthesis conditions of the solid‐phase sintering method limit its application in the field of high‐level radioactive waste solidification. In this study, 5 wt.% CaO was added as a mineralizing agent. The synthesis conditions were optimized, achieving a reduced protocol of 1500°C with a dwelling time of 6 h. To understand this catalytic effect, XRD analysis identified that CaO facilitates the phase transition from m‐ZrO ₂ to t‐ZrO ₂ , which is the primary mechanism for reducing the synthesis temperature and duration. Based on this, a series of Zr _{(1‐ x )} Ce _x SiO ₄ (0 < x < 0.4) waste forms, with CeO ₂ simulating tetravalent actinides, were synthesized at a substantially lower temperature. A stable solid solution formed for x ≤ 0.35, evidenced by a single‐phase zircon structure coexisting with m‐Zr _{(1‐ x )} Ce _x O ₂ , confirming effective Ce ⁴⁺ replacement of Zr ⁴⁺ within the structural tolerance. Beyond x > 0.35, the structure was compromised due to peak broadening and secondary phases, indicating the maximum accommodation capacity was reached. The optimal formulation ( x = 0.35) was subsequently used to produce a glass‐ceramic waste form with iron phosphate glass. Higher glass content was found to consistently improve immobilization efficiency and reduce leaching rates. The form showed exceptional durability, with a Ce ⁴⁺ leaching rate of only 2.67×10 ⁻⁶ g·m ⁻² ·d ⁻¹ (28 days, 90°C), confirming the promise of this strategy for advanced ZrSiO ₄ ‐based actinide waste forms.